1. Field of the Invention
The present invention relates to a semiconductor device, and more particularly to a semiconductor device containing a CCD chip.
2. Description of the Related Art
Heretofore, a semiconductor device has been known in the art wherein a ceramic package thereof has a recess portion in which a semiconductor element such as a CCD (Charge Couple Device) chip is contained, and the recess portion is covered with a cap. The portion of the cap that is bonded to the package is usually made of ceramic, metal or the like, while the portion of the cap facing to the CCD chip is made of transparent glass, in consideration of a case in which the CCD chip is used as imaging means or optical sensors. Although a semiconductor device having such a construction exhibits a high strength since the package and the cap are made of ceramic or glass, the device has a drawback of an increased manufacturing cost.
On the other hand, Japanese Patent Laid-open No.145748/87 discloses a semiconductor device whose package is made of a plastic. The manufacturing cost of this construction is lower than that of the construction in which the package is made of ceramic.
Thus, in the disclosed semiconductor device, reduction in cost may be achieved by forming the package from a plastic. However, since glass must be inserted in the cap in order to allow light to be incident on the CCD chip, an increase in cost results. Therefore, from the viewpoint of reduction in cost, it is desirable that the package and cap of the semiconductor device are made of plastic and glass rather than ceramic and glass, and it is more desirable that all portions are exclusively made of a plastic.
However, there is a problem in manufacture when package 11 and cap 15 of a semiconductor device are exclusively made of a plastic as shown in FIGS. 1A, 1B and 1C. In general, a semiconductor device is mounted on printed circuit board 14 for use. As shown in FIG. 1B, leads 13 of the semiconductor device is inserted into though holes 14a of printed circuit board 14, and immersed into molten solder bath 16 at a high temperature and then they are cooled, thereby solidifying solders 16a to cause the semiconductor device to be fixed to printed circuit board 14. In such a so-called flowing process, heating and cooling are performed while the semiconductor device is mounted on printed circuit board 14. At this time, if the thermal expansion coefficients are different between the semiconductor device and printed circuit board 14, then the magnitudes of expansion and contraction are different between the semiconductor device and printed circuit board 14, thereby causing warp as shown in FIG. 1C. In particular, after solder 16a is cooled and solidified (when the temperature is equal to or lower than the eutectic temperature 183.degree. C.), the semiconductor device and printed circuit board 14 will contract at different rates while both are fixed at the portions of leads 13 so that an unnatural deformation occurs and a large warp is generated.
When the semiconductor device having the warp generated in this way is used as a sensor for reading images in a scanner or as imaging means, the error is large, and therefore the accuracy is deteriorated.